1. Field of the Invention
This invention relates to semi-processed non-oriented electromagnetic steel strips having a low core loss and a high magnetic permeability.
2. Prior Art
It is a common practice to lower the core loss of electromagnetic steel strip by adding silicon (Si) and aluminum (Al) to the steel composition to increase the resistivity and reduce the eddy current loss thereof. Addition of these elements is effective in lowering the core loss, but undesirably results in a reduced magnetic permeability.
Japanese Patent Publication No. 56-34616 proposes the addition of manganese (Mn) instead of Si and Al. The addition of manganese is effective in increasing resistivity while reducing magnetic permeability to a relatively less extent. However, magnetic permeability is reduced with the addition of manganese although it is a relatively small reduction.
Japanese Patent Application Kokai No. 61-67753 proposes to reduce the core loss of electric steel by adding copper (Cu) to modify its aggregate texture. With this method, however, magnetic permeability is more or less reduced. Since copper has a low melting point, there remains a risk that hot brittle cracking would occur during hot rollding.
A variety of methods have been employed to manufacture electrical steel having improved magnetic properties. With respect to a hot rolling step, Japanese Patent Application Kokai No. 51-74923 proposes a method for manufacturing an electrical steel strip having improved magnetic properties and a minimized variation in thickness by completing hot rolling at as high a temperature in the ferrite region as possible. Japanese Patent Application Kokai No. 57-35628 proposes to complete hot rolling at a temperature in the austenite region and carry out annealing at a temperature in the ferrite region for 30 seconds to 15 minutes for the purpose of increasing the grain size before cold rolling to eventually improve magnetic properties. Further, Japanese Patent Application Kokai No. 49-38814 discloses that magnetic properties are improved by heating a slab at a temperature of lower than 1,200.degree. C. to precipitate coarse grains of AlN to promote the growth of grains.
However, there is available no adequate composition or manufacturing method which is successful in reducing core loss and increasing magnetic permeability.